By Amy Grant I grew up in an area near an old apple orchard and the old gnarled trees were something to see, like great arthritic old ladies anchored into the earth. I always wondered about the knobby growths on the apple trees and since then have discovered that there are a couple of things that can cause them. Read on to learn more these apple tree growths. Apple Tree Burr Knots Burr knots on apple trees are particularly common on some apple varieties, especially early “June” cultivars. Apple tree burr knots (also spelled burrknots) are clumps of twisted or knobby growths on apple trees branches, usually when they are three years old or older. This occurrence increases on dwarf rootstocks. The outgrowths can produce both shoots and roots, so if you want to start another tree, you need only prune the affected branch from the mother and plant it.